One known high-temperature steel used in boiler making is 10 CrMo 9 10 steel, which corresponds approximately to grade T 22 of ASTM A 199, 200 and 213 as well as grade P 22 of ASTM A 335, and contains the following alloy elements (wt. %):
C 0.080 to 0.150%
Si .ltoreq.0.50%
Mn 0.40 to 0.70%
P .ltoreq.0.035%
S .ltoreq.0.035%
Cr 2.00 to 2.50%
Mo 0.90 to 1.20%
The high-temperature strength of this steel is sufficient for many uses but does not meet the higher demands for certain applications. For high stresses, high-alloy steels are frequently used, such as, for example, the high-temperature steel X 20 CrMo V 12 1, which contains 12% chromium. However, these steels are both expensive and difficult to work with.
A high strength, heat-resistant steel alloy is disclosed in European Patent 0 411 515 A1 which has the following alloy elements (wt. %):
C 0.030 to 0.120%
Si .ltoreq.1.0%
Mn 0.20 to 1.00%
P .ltoreq.0.030%
S .ltoreq.0.030%
Ni .ltoreq.0.8%
Cr 0.7 to 3.0%
Mo 0.30 to 0.70%
W 0.6 to 2.4%
V 0.05 to 0.35%
Nb 0.01 to 0.12%
N 0.10 to 0.50%
In this alloy, the proportions of W and Mo satisfy the following relationship: EQU 0.8% .ltoreq.(Mo %+1/2W %).ltoreq.1.5%
The manufacture of such steel is considerably expensive due in particular to the requirement that the W is homogeneously distributed. Furthermore, due to the high resistance to deformation to different coatings, difficulties are encountered with respect to hot shaping, for instance, upon the rolling of seamless robes. There is thus a need for a high-temperature steel which has very high values of high-temperature strength but also can be produced at relatively little cost and can be readily processed further.